I run Power Service grey bottle every tank full although the stuff seems to do what it's intended to do, but I'm looking to switch to Opti-Lube XPD since it's was rated higher on the lubricity study. The PS seems to really help with the every day injector clatter and gets me pretty good mpg's for daily driving. I have found Opti-Lube XPD on Amazon in gallons or 8oz bottles; I was trying to go away from having to always measure out the prescribed amount of additive all the time so leaning towards the 8oz bottles and the Opti-Box to have a spill proof place for them behind the back seat and have them with me for each fill up. My question for those that use Opti-Lube is the optimal mix ratio in the study was 13oz per 26 gallon but each 8oz bottle says it treats up to 32 gallons, am I missing something here? The study was dated 2007, has Opti-Lube changed their formula so that an 8oz bottle now does what 13oz did back then? Any advice is helpful.